Classifications

• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08G—MACROMOLECULAR COMPOUNDS OBTAINED OTHERWISE THAN BY REACTIONS ONLY INVOLVING UNSATURATED CARBON-TO-CARBON BONDS
  • C08G63/00—Macromolecular compounds obtained by reactions forming a carboxylic ester link in the main chain of the macromolecule
  • C08G63/88—Post-polymerisation treatment
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
  • B29C—SHAPING OR JOINING OF PLASTICS; SHAPING OF MATERIAL IN A PLASTIC STATE, NOT OTHERWISE PROVIDED FOR; AFTER-TREATMENT OF THE SHAPED PRODUCTS, e.g. REPAIRING
  • B29C64/00—Additive manufacturing, i.e. manufacturing of three-dimensional [3D] objects by additive deposition, additive agglomeration or additive layering, e.g. by 3D printing, stereolithography or selective laser sintering
  • B29C64/10—Processes of additive manufacturing
  • B29C64/141—Processes of additive manufacturing using only solid materials
  • B29C64/153—Processes of additive manufacturing using only solid materials using layers of powder being selectively joined, e.g. by selective laser sintering or melting
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B33—ADDITIVE MANUFACTURING TECHNOLOGY
  • B33Y—ADDITIVE MANUFACTURING, i.e. MANUFACTURING OF THREE-DIMENSIONAL [3-D] OBJECTS BY ADDITIVE DEPOSITION, ADDITIVE AGGLOMERATION OR ADDITIVE LAYERING, e.g. BY 3-D PRINTING, STEREOLITHOGRAPHY OR SELECTIVE LASER SINTERING
  • B33Y70/00—Materials specially adapted for additive manufacturing
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B33—ADDITIVE MANUFACTURING TECHNOLOGY
  • B33Y—ADDITIVE MANUFACTURING, i.e. MANUFACTURING OF THREE-DIMENSIONAL [3-D] OBJECTS BY ADDITIVE DEPOSITION, ADDITIVE AGGLOMERATION OR ADDITIVE LAYERING, e.g. BY 3-D PRINTING, STEREOLITHOGRAPHY OR SELECTIVE LASER SINTERING
  • B33Y70/00—Materials specially adapted for additive manufacturing
  • B33Y70/10—Composites of different types of material, e.g. mixtures of ceramics and polymers or mixtures of metals and biomaterials
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
  • B29K—INDEXING SCHEME ASSOCIATED WITH SUBCLASSES B29B, B29C OR B29D, RELATING TO MOULDING MATERIALS OR TO MATERIALS FOR MOULDS, REINFORCEMENTS, FILLERS OR PREFORMED PARTS, e.g. INSERTS
  • B29K2067/00—Use of polyesters or derivatives thereof, as moulding material
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B33—ADDITIVE MANUFACTURING TECHNOLOGY
  • B33Y—ADDITIVE MANUFACTURING, i.e. MANUFACTURING OF THREE-DIMENSIONAL [3-D] OBJECTS BY ADDITIVE DEPOSITION, ADDITIVE AGGLOMERATION OR ADDITIVE LAYERING, e.g. BY 3-D PRINTING, STEREOLITHOGRAPHY OR SELECTIVE LASER SINTERING
  • B33Y10/00—Processes of additive manufacturing

Definitions

• the present invention generally pertains to a build material and a semi-crystalline polymer useful for additive manufacturing applications.
• 3-D printing also known in the art as additive manufacturing, refers to a class of processes for the production of three-dimensional objects wherein multiple layers of a material known as a“build material” are applied to a bed or substrate on a layer-by-layer basis.
• a“build material” Such processes are particularly useful in the manufacture of prototypes, models and molds; however, more recently these processes have been increasingly utilized for production parts, consumer products, medical devices and the like.
• laser sintering involves applying a layer of powdered or pulverulent polymer material to a target or build surface; heating a portion of the material; irradiating selected or desired part locations/shape with laser energy to sinter those portions and produce a part“slice”; and repeating these steps multiple times (the repetition often referred to as the“build”) to create useful parts in the form of sequentially formed, multiple fused layers.
• Laser sintering is described for example in U.S. Patent Nos. 6,100,41 1 ; 5,990,268 and 8,1 14,334, the descriptions and disclosure of which are hereby incorporated herein by reference.
• Additive manufacturing processes that utilize other irradiation energy sources such as infrared radiation are also known in the art. Fusion could be complete or partial fusion.
• 9,580,551 notes that if the system maintains the bed of powder at a temperature that is too low (e.g., too near such powder's recrystallization point), then the fused powder may return to a solid state (or“recrystallize”) too quickly, which may cause the formed object to warp or deform.
• This patent further notes that, if the system maintains the bed of powder at a temperature that is too high (e.g., too near such powder's melting point), then the remaining unfused powder may partially melt, which may increase the relative difficulty of separating the remaining unfused powder from the formed object. This difficulty of separating in turn reduces the recyclability of the material or the ability to reuse the material.
• a different temperature results in regions of the just- sintered initial slice of powder which will either cause an already sintered slice to melt and be distorted in a layer of the part bed which has "caked"; or, will cause an already sintered slice to curl if the part bed temperature is too low.
• Nylon 12 Many laser sintering printers were designed for Nylon 12 which can be formed into a powder that has a very narrow and well-defined melting temperature. To find utility in such powder laser sintering printers a polymer must be designed to have thermal properties similar to Nylon 12. However, even Nylon 12 has some drawbacks in that the printed layer must be kept at a relatively high temperature and then cooled slowly or the polymer will recrystallize too quickly and distort the part.
• thermal annealing is challenging as the temperature required to most rapidly anneal is significantly above Tg, commonly at least 140 °C. Increasing the temperature above Tg causes pellets to stick together.
• External plasticizers can cause crystallization but cause deposits and condensate issues in printers.
• Solvent crystallization has been attempted but clumping, or caking, occurs during printing. It has now been found that polymers that could not previously be used successfully for laser sinter printing can be processed to yield powder that prints in a variety of printers.
• a build material for additive manufacturing applications includes a build composition in powder form.
• the build composition includes a semi crystalline polymer having a glass transition temperature of at least 70 °C, an onset melting temperature of at least 125 °C, a Tm of at least 170 °C, and a dHf of at least 21 J/g, all measured using DSC.
• the semi crystalline polymer is a crystallized amorphous polymer that exhibits an amorphous return.
• the semi-crystalline polymer has a glass transition temperature from 70 °C to 200 °C, an onset melting temperature from 125 °C to 10 °C below the Tm, a Tm from 170 °C to 275 °C, and a dHf from 21 J/g to 40 J/g.
• a semi-crystalline polymer useful in additive manufacturing applications has having a glass transition temperature of at least 70 °C, an onset melting temperature of at least 125 °C, a Tm of at least 170 °C, and a dHf of at least 21 J/g, all measured using DSC.
• the semi-crystalline polymer is a crystallized amorphous polymer that exhibits an amorphous return.
• the polymer may be in the form of a powder and/or may be a component of a polymer composition that is in the form of a powder.
• a method for making an additive manufacturing polymer includes the steps of:
• the amorphous polymer pellets have a Tg of at least 70 °C.
• the amorphous polymer is a copolyester.
• the crystalline shell has a thickness of 15% or less, or 10% or less, of the pellet diameter.
• Figure 1 is a graph showing DSC heating and cooling scans of Nylon 12.
• Figure 2 is a graph showing DSC thermograms for solvent annealed vs. solvent and thermal annealed pellets.
• Figure 3 is a plot showing an example for calculating dHf.
• Figure 4 is a graph showing DSC heat-cool-heat thermograms of solvent and thermally annealed polymer powder.
• Figure 5 is a graph showing relative average wall thickness of a crystalline shell of a polymer as a function of time of exposure to acetone.
• Figure 6 is a graph showing copolyester dHf as a function of time in acetone.
• Figure 7 is graph showing heat of fusion as a function of time at 170 °C for copolyester samples.
• Figure 8 is graph showing a crystallized copolyester DSC heat- cool-heat thermograms.
• a polymer is provided that is useful for selective laser sintering additive manufacturing (SLS-AM).
• SLS-AM selective laser sintering additive manufacturing
• the polymer useful for SLS-AM can be printed using processes/equipment primarily designed/configured for polyamide 12 (PA12) (or Nylon 12).
• PA12 polyamide 12
• Nylon 12 polyamide 12
• such a process can be as follows: a room temperature build material powder is added to a printer bed where temperature can be controlled from room temperature up to and beyond 170 °C, which are common PA12 bed temperatures. A thin layer of heated powder is rolled out to the print bed where the design of that layer is sintered using a high energy laser.
• the laser raises the temperature of the powder above the melting point, commonly greater than 200 °C.
• the part bed (being formed layer by layer) is lowered and the next layer is spread onto the part bed and the process is repeated until the print is completed. Final sintered parts are then removed from the powder bed.
• the thermal profile of the polymer matches that of polyamide 12 (PA12), such that it can be dropped into an SLS printer designed for PA12.
• DSC heating and cooling thermograms for Nylon 12 are shown in Figure 1 where a 175 °C melting peak and a 140 °C crystallization peak are shown.
• a copolyester is provided that matches this melting temperature sufficiently to allow a copolyester powder to be printed using an SLS printer designed for PA12.
• a build material that includes a build composition in powder form.
• a suitable particle size range for the powder form of the build material is between 20 and 200 urn as measured by DLS and a suitable median for the volume particle size distribution (referred to as D [50]) is from 40 to 80 pm as measured by dynamic light scattering (DLS).
• the build composition is present in the build material in the amount of from 40% to 100% by volume of the build material based on the total volume of the solids fraction of the build material.
• Additional but optional ingredients in the build material include one or more of crystallizing agents such as nucleating agents; colorants; heat and/or light stabilizers; heat absorbing agents such as heat absorbing inks; anti-oxidants, flow aids, and filler materials such as glass, mineral, carbon fibers and like.
• the build material is the build composition in polymer form. Accordingly, in an embodiment, the build material may consist essentially of or consist of the build composition in powder form.
• the build composition includes a semi-crystalline polymer which is a component of the build composition.
• “Semi-crystalline” is defined as a polymer with crystallinity level determined by a heat of fusion or dHf of 2J/g or more, as measured by DSC.
• “Amorphous” is defined as a polymer with a dHf of less than 2J/g, as measured by DSC. Beyond melting point the glass transition temperature can be important in considering copolyesters for additive manufacturing, e.g., SLS-AM. Higher glass transition temperatures yield a higher zero shear melt viscosity and glass transition temperature also plays a role in crystallization kinetics.
• crystallization kinetics can be characterized using the Fastest Crystallization Halftime (FCH), where polyesters with a fast crystallization half time are, for practical purposes, semi-crystalline.
• FCH Fastest Crystallization Halftime
• ssignificantly long FCH results in a practically amorphous polymer that does not crystallize under traditional melt processing methods such as injection molding, extrusion, or blow molding.
• the semi-crystalline polymers can have a glass transition temperature (T g ) of at least 70 °C and FCH less than 200 minutes, or less than 150 minutes.
• T g glass transition temperature
• the semi-crystalline polymers are chosen from polyesters, copolyesters, polycarbonates, polyamides and polyether ketones, provided such polymers exhibit amorphous return.
• Particularly suitable semi-crystalline polymers have a crystallinity of determined by a dHf from 21 to 40 J/g.
• the semi-crystalline polymer has a FCH of from 10 to 150 minutes, or 15 to 150 minutes, or 20 to 150 minutes.
• the semi-crystalline polymer is present in the build composition in an amount of from 60% to 100% by volume of the build composition based on the total volume of the solids fraction of the build composition.
• the semi-crystalline polymer is in the form of a powder and the build composition is a semi-crystalline polymer (as described herein) in powder form.
• the build composition may consist essentially of or consist of the semi-crystalline polymer in powder form.
• the semi-crystalline polymer in one embodiment is a crystallized amorphous polymer.
• “Crystallized amorphous polymer” is defined herein as a semi-crystalline polymer formed through inducement of crystalline structure starting from an amorphous polymer through solvent annealing and/or thermal annealing crystallization. Crystallized amorphous polymers have a crystallinity level higher than that of the polymer before the crystallinity inducement process. Other methods for inducing crystalline structure in generally amorphous polymers are known in the art, including for example solvent precipitation crystallization, thermal crystallization and strain crystallization and the like.
• Solvent annealing crystallization involves exposing a polymer to a low molecular weight (below about 500 g/mol) solvent vapor or solvent liquid to swell the polymer without substantially dissolving it or causing the polymer pellets to stick together. Selection of a suitable solvent for solvent annealing crystallization will depend in part on the polymer type to be crystallized. For example, acetone or methyl acetate are suitable choices of solvent for copolyesters and may be used either in pure form or as part of an aqueous system. A partially miscible solvent system can also be used to expand the range of solvent choices.
• the polymer can be maintained at the solvent crystallization temperature or a series of increasing crystallization temperatures below the melting temperature until the desired level of crystallinity has been achieved.
• the solvent crystallization can be performed at room temperature. Any residual solvent can be removed via thermal and/or vacuum treatments.
• the polymer may also be heated to a temperature at which crystallization is faster than at the solvent exposure temperature. Nucleation agents may also be incorporated via compounding or some other process to promote or control crystallization of the amorphous polymer.
• a process for making a semi-crystalline polymer where solvent annealing and thermal annealing are combined to yield semi-crystalline pellets that do not stick together at temperatures between Tg and Tm.
• Tm refers to highest temperature of an endothermic peak apex on the DSC first heating curve (measured at a heating rate of 20 °C/min).
• Tm is the peak of the highest temperature, after deconvolution of the multiple peaks.
• Solvent crystallization causes crystallization progressing through the outer surface of crystallizable copolyesters.
• pellets having a crystallized surface shell will appear hazy while the interior of the pellet will remain amorphous.
• solvent crystallization can be performed on copolyesters with FCH less than 200 minutes. It has been discovered that copolyesters with FCFI too high will swell in solvent and stick together during solvent exposure. It was also discovered that thermal annealing amorphous copolyester pellets without first solvent annealing the surface results in the pellets sticking together.
• the polyesters have an FCFI of less than 200 minutes, or less than 150 minutes. In embodiments, the polyesters have an FCFI of more than 10 minutes, or more than 1 5 minutes, or more than 20 minutes.
• the polyesters have an FCFI from 10 to 200 minutes, or 10 to 150 minutes, or 10 to 100 minutes, or 10 to less than 100 minutes, or 15 to 200 minutes, or 15 to 150 minutes, or 15 to 100 minutes, or 15 to less than 100 minutes, or 20 to 200 minutes, or 20 to 150 minutes, or 20 to 100 minutes, or 20 to less than 100 minutes.
• amorphous polymer pellets without solvent annealing results in the pellets sticking together during thermal annealing.
• solvent annealing the pellets alone i.e., solvent annealing too much or without subsequent thermal annealing
• thermal annealing the pellets alone i.e., without surface solvent annealing
• Pellets that are solvent annealed for 24 hours showed poor thermal behavior where a distinct melting peak was not apparent.
• Figure 2 shows the differences in melting peak shape after exposure to solvent and after thermal exposure for Polymer 1 .
• the semi-crystalline polymer component of the build composition of the present invention may be characterized by (i) a glass transition temperature (T g ) of at least 70 °C, (ii) an onset melting temperature of at least 125 °C, (iii) a Tm of at least 170 °C, and (iv) a dHf of at least 21 J/g, all measured using DSC.
• the semi-crystalline polymer is a crystallized amorphous polymer that exhibits an amorphous return.
• the polymer may be in the form of a powder and/or may be a component of a polymer composition that is in the form of a powder.
• pellets manufactured using solvent and thermal annealing processes as described herein can be cryoground to powder less than 100 microns, and then parts can be printed from the powder.
• Glass transition temperature is the temperature at which the mechanical properties of a polymer fairly rapidly change glassy to rubbery due to the internal movement of the polymer chains that form the polymer. This change in behavior is typically measured by Differential Scanning Calorimetry (DSC) techniques known in the art and is evidenced for example by a sharp decline in modulus (stiffness) or increase in impact strength as the ambient temperature is increased. Glass transition temperature is measured according to the methods known in the art, such as ASTM E1356 - 08(2014). In embodiments, suitable semi-crystalline polymers for the build composition of the present invention have a glass transition temperature of from 70 °C to 120 °C, or 75 °C to 90 °C, or 90 °C to 120°C.
• FCH Fastest crystallization half-time
• T c the crystallization temperature
• FCFI is typically at its minimum, i.e., maximum crystallization rate, at a temperature approximately half way between the glass transition temperature (T g ) and the melt temperature (Tm).
• SALS small angle light scattering
• a sample is first melted at a temperature well above the melt temperature to remove all preexisting crystallinity. Then, the sample is rapidly cooled to a predetermined temperature (T ⁇ oi) and the scattered light intensity is recorded as a function of time. The time at which the scattered light intensity increases to half the maximum value denotes the crystallization half-time reported. As crystallization rate varies with temperature, the temperature at which the crystallization rate is the highest in this range (corresponding to the temperature with the fastest crystallization half-time in the temperature range) was chosen to quantify the parameter for comparison purposes hereunder.
• Crystallinity level is an indicator of the level of crystalline domains in a polymer. Crystallinity level can be measured by using DSC and the enthalpy of fusion of the polymer. Crystallinity is measured according to methods known in the art, for example as described in ASTM D3418 - 15. The degree of crystallization can be determined using a differential scanning calorimeter and plotting heat flow versus temperature and heating the sample in N2 purge at 20 °C/min from RT to 290 °C.
• Crystalline content is defined here as the heat of fusion determined according to ASTM D3418 - 15 section 1 1 from the plot of heat flow versus temperature using the area of the melting endotherm, in J/g, where the baseline is interpolated from the steady state heat flow (i.e., the area of the curve under the dashed line).
• An example of the dHf area determination for PA12 is shown in Figure 3.
• semi-crystalline polymers can be chosen from polyesters, copolyesters, polycarbonates, polyamides, polyether ketones and copolymers thereof, provided such polymer(s) exhibit amorphous return.
• the semi-crystalline polymers can be chosen from polyesters or copolyesters.
• Particularly suitable semi-crystalline polymers are polyesters, which includes copolyesters. In general, such polyesters are formed from one or more acids and one or more glycols (also referred to in the art as diols).
• the acid component can in some cases include a diacid component and can include for example units derived from a terephthalic acid (TPA), units derived from an isophthalic acid (IPA), units derived from a cyclohexanedicarboxylic acid, units derived from a naphthalene dicarboxylic acid, units derived from a stilbenedicarboxylic acid, units derived from furandicarboxylic acid, or combinations thereof.
• TPA terephthalic acid
• IPA isophthalic acid
• the acid component can include units of a first acid and units of one or more second acids.
• the first acid can include terephthalic acid and, in addition, one or more second acids can be selected from a group of diacids including isophthalic acid, 1 ,3-cyclohexanedicarboxylic acid, 1 ,4cyclohexanedicarboxylic acid, a naphthalenedicarboxylic acid, a stilbenedicarboxylic acid, furandicarboxylic acid, sebacic acid, dimethylmalonic acid, succinic acid, or combinations thereof.
• diacids including isophthalic acid, 1 ,3-cyclohexanedicarboxylic acid, 1 ,4cyclohexanedicarboxylic acid, a naphthalenedicarboxylic acid, a stilbenedicarboxylic acid, furandicarboxylic acid, sebacic acid, dimethylmalonic acid, succinic acid, or combinations thereof.
• the naphthalenedicarboxylic acid can include 1 ,4-naphthalenedicarboxylic acid, 1 ,5-naphthalenedicarboxylic acid, 2,6-naphthalenedicarboxylic acid, or 2,7- naphthalenedicarboxylic acid.
• the furandicarboxylic acid can include 2, 5-furandicarboxylic acid.
• the glycol component can include units derived from cyclohexanedimethanol (CFIDM), ethylene glycol (EG), 2,2,4,4-tetramethyl-1 ,3- cyclobutanediol (TMCD), propane diol, isosorbide, spiro-glycol (SPG), or combinations thereof.
• CFIDM cyclohexanedimethanol
• EG ethylene glycol
• TMCD 2,2,4,4-tetramethyl-1 ,3- cyclobutanediol
• propane diol propane diol
• isosorbide propane diol
• SPG spiro-glycol
• polyesters made with EG may contain up to 5 mole%, or up to 4 mole%, or less DEG units (or residues).
• the glycol component can include units derived from a first glycol and units derived from one or more second glycols.
• the first glycol can include cyclohexanedimethanol and the one or more second glycols can include one or more glycols including about 2 to about 20 carbon atoms.
• the one or more second glycols can include ethylene glycol, 2,2,4,4-tetramethyl-1 ,3-cyclobutanediol, 1 ,2-propanediol, 1 ,3- propanediol, neopentyl glycol, 1 ,4-butanediol, 1 ,5-pentanediol, 1 ,6-hexanediol, p-xylene glycol, spiro-glycol, isosorbide, or combinations thereof.
• Polyesters as well as suitable acids and glycols for forming them, are generally described for example in U.S. Published Patent Application Nos. 2012/0329980 and 2017/0066873, both assigned to the assignee of the present invention, the contents and disclosure of which are hereby incorporated herein by reference.
• the build material for additive manufacturing applications includes a build composition in powder form and the build composition includes a semi-crystalline copolyester having a glass transition temperature of at least 70 ° C, with the semi-crystalline copolyester including 55 to 100 mole % terephthalic acid residues and 30 to 100 mole % CHDM residues,
• the polyester comprises:
• the dicarboxylic acid component comprises 20 to 45 mole percent, 20 to 42 mole percent, or 20 to 40 mole percent, or 20 to 35 mole percent, or 20 to 30 mole percent, or 30 to 45 mole percent, or 30 to 42 mole percent, or 30 to 40 mole percent of IPA residues.
• the balance of the dicarboxylic acid component is TPA resides.
• the glycol component comprises 90 to 100 mole percent, or 95 to 100 mole percent, or 96 to 100 mole percent, or 100 mole percent of CHDM residues.
• the inherent viscosity of the polyester is from 0.1 to 1.2 dL/g as determined in 60/40 (wt/wt) phenol/tetrachloroethane at a concentration of 0.5 g/100 ml at 25 ° C.; and the polyester has a Tg of from 70 to 100 ° C.
• the polyester comprises:
• EG ethylene glycol
• the glycol component comprises CHDM residues in an amount from 15 to 60 mole%, or 15 to 56 mole%, or 15 to 55 mole%, or 15 to 50 mole%, or 15 to 45 mole%, or 15 to 40 mole%, or 15 to 35 mole%, or 15 to
• the glycol component comprises CHDM residues in an amount from 30 to 60 mole%, or
• the balance of the glycol component can be essentially EG residues. It should be understood that the glycol component may also include DEG residues, e.g., in amounts formed in-situ. In embodiments, the glycol component comprises DEG residues in an amount from 0.1 to 5 mole%, or 0.1 to 4 mole%, or 0.1 to 3 mole%.
• the polyester comprises:
• TMCD 2,2,4,4-tetramethyM ,3-cyclobutanediol
• the inherent viscosity of the polyester is from 0.1 to 1.2 dL/g as determined in 60/40 (wt/wt) phenol/tetrachloroethane at a concentration of 0.5 g/100 ml at 25 ° C.; and wherein the polyester has a Tg of from 80 to 120° C.
• the glycol component comprises TMCD residues in an amount from 15 to 60 mole%, or 15 to 56 mole%, or 15 to 55 mole%, or 15 to 50 mole%, or 15 to 45 mole%, or 15 to 40 mole%, or 15 to 35 mole%, or 15 to
• the balance of the glycol component can be CHDM residues.
• any one of the polyesters or polyester compositions described herein can further comprise residues of at least one branching agent. In embodiments, any one of the polyesters or polyester compositions described herein can comprise at least one thermal stabilizer or reaction products thereof.
• the polyester composition contains at least one polycarbonate. In other embodiments, the polyester composition contains no polycarbonate.
• the polyesters useful in the invention contain less than 15 mole % ethylene glycol residues, such as, for example, 0.01 to less than 15 mole % ethylene glycol residues. In embodiments, the
• polyesters useful in the invention contain less than 10 mole %, or less than 5 mole %, or less than 4 mole %, or less than 2 mole %, or less than 1 mole % ethylene glycol residues, such as, for example, 0.01 to less than 10 mole %, or 0.01 to less than 5 mole %, or 0.01 to less than 4 mole %, or 0.01 to less than 2 mole %, or 0.01 to less than 1 mole %, ethylene glycol residues.
• the polyesters useful in the invention contain no ethylene glycol residues.
• the polyesters useful in the invention are made from no 1 ,3-propanediol, or, 1 ,4-butanediol, either singly or in combination. In other aspects, 1 ,3-propanediol or 1 ,4-butanediol, either singly or in
• 2,2,4,4-tetramethyl-1 ,3-cyclobutanediol useful in certain polyesters useful in the invention is greater than 50 mole % or greater than 55 mole % of cis-
• the mole % of the isomers of 2,2,4,4-tetramethyM ,3-cyclobutanediol useful in certain polyesters useful in the invention is from 30 to 70 mole % of cis-2,2,4,4-tetramethyl-1 ,3- cyclobutanediol or from 30 to 70 mole % of trans-2,2,4,4-tetramethyl-1 ,3- cyclobutanediol, or from 40 to 60 mole % of cis-2,2,4,4-tetramethyl-1 ,3- cyclobutanediol or from 40 to 60 mole % of trans-2,2,4,4-tetramethyl-1 ,3- cyclobutanediol, wherein the total mole percentage of cis-2,2,4,4-tetramethyl- 1 ,3-cyclobutanediol and trans-2,2,4,4-t
• the semi-crystalline polymer has a glass transition temperature of at least 70 °C, an onset melting temperature of at least 125 °C, a Tm or at least 170 °C, and a dHf of at least 21 J/g, all measured using DSC.
• the Tg of the polymer can be at least one of the following ranges: 70 to 120 °C; 70 to 1 15 °C 70 to 1 10 °C; 70 to 105 °C; 70 to 100 °C; 70 to 95 °C; 70 to 90 °C; 70 to 85 °C; 75 to 120 °C; 75 to 1 15 °C; 75 to 1 10 °C; 75 to 105 °C; 75 to 100 °C; 75 to 95 °C; 75 to 90 °C; 80 to 120 °C; 80 to 115°C; 80 to 110°C; 80 to 105°C; 80 to 100 ⁇ ; 80 to 95 °C; 80 to 90 °C; 85 to 120°C; 85 to 115°C;85 to 110°C;85 to 105 ⁇ :85 to 100°C;85 to 95°C;90 to 120°C; 90 to 115°C;90 to 110°C;90 to 105 ⁇ :90 to 100°C;95 to 120°C;
• the onset melting temperature of the semi crystalline polymer can be at least one of the following ranges: 125 to 10°C below the Tm; 125 to 220 °C; 125 to215°C; 125 to210°C; 125 to 205 °C; 125 to 200 °C; 125 to 195 ⁇ ; 125 to 190°C; 125 to 185°C; 125 to 180°C; 125 to 175°C; 125 to 170°C; 125 to 165 °C; 125 to 160 °C; 125 to 155 °C; 125 to
• the Tm of the semi-crystalline polymer can be at least one of the following ranges: 170 to 225 °C; 170 to 220 °C; 170 to 215°C; 170 to210°C; 170 to 205 °C; 170 to 200 °C; 170 to 195°C; 170 to
• the Tm of the semi-crystalline polymer can be at least one of the following ranges: 225 to 275 °C; 225 to 270 °C; 225 to 265 °C; 225 to 260 °C; 225 to 255 °C; 225 to 250 °C; 225 to 245 °C; 225 to 240 °C; 225 to 235 °C; 230 to 275 °C; 230 to 270 °C; 230 to 265 °C; 230 to 260 °C; 230 to 255 °C; 230 to 250 °C; 230 to 245 °C; 230 to 240 °C; 235 to 275 °C; 235 to 270 °C; 235 to 265 °C; 235 to 260 °C; 235 to 255 °C; 235 to 250 °C; 230 to 245 °C; 230 to 240 °C; 235 to 275 °C; 235
• the polyesters useful in the invention may exhibit at least one of the following inherent viscosities as determined in 60/40 (wt/wt) phenol/tetrachloroethane at a concentration of 0.5 g/100 ml at 25° C.: 0.10 to 1.2 dL/g; 0.10 to 1.1 dL/g; 0.10 to 1 dL/g; 0.10 to less than 1 dL/g; 0.10 to 0.98 dL/g; 0.10 to 0.95 dL/g; 0.10 to 0.90 dL/g; 0.10 to 0.85 dL/g; 0.10 to 0.80 dL/g; 0.10 to 0.75 dL/g; 0.10 to less than 0.75 dL/g; 0.10 to 0.72 dL/g; 0.10 to 0.70 dL/g; 0.10 to less than 0.70 dL/g; 0.10 to 0.68 dL/g; 0.10 to less than 0.68 dL/g
• the method includes the steps of:
• the solvent annealing is performed under conditions to provide a semi-crystalline shell having the minimum thickness to prevent pellets from sticking together in the thermal annealing step.
• the semi-crystalline shell has a thickness that is less than 10%, or less than 5%, or less than 4%, or less than 3%, or less than 2%, or less than 1 %, or less than 0.5% of the diameter of the solvent annealed pellet.
• the solvent annealed pellets have a dHf of at least 3 J/g, or at least 4 J/g, or at least 5 J/g.
• the solvent annealed pellets have a dHf from 25 to 50% of the dHf of the thermally annealed pellets (in J/g).
• the solvent annealing is carried out by contacting the pellets with solvent for 15 minutes to 2 hrs, or 30 minutes to 1 hour at a temperature from 15 °C to 50 °C, or 15 °C to 30 °C. In embodiments, the solvent annealing is carried out by contacting the pellets with solvent using 10 to 100 parts solvent per 100 parts pellets, or 10 to 50 parts solvent per 100 parts pellets (by weight).
• the polymer is a polyester and solvent is acetone.
• the thermal annealing step is carried out at a temperature from the Tg to 10°C below the Tm, or 70 °C to 200 °C, or 80 °C to 190 °C, or 80 °C to 180*C, or 80 °C to 170°C, or 90°C to 160°C, or 100 °C to 150 °C, or 120 °C to 150 °C, or 130 °C to 150 °C. In one embodiment, the thermal annealing step is carried out at a temperature within 10°C of the TCH.
• the thermal annealing step is carried out for a time sufficient to achieve a dHf within 10% of the maximum dHf obtainable by heating for up to 24 hrs. In embodiments, the thermal annealing step is carried out for a time from 30 minutes to 10 hrs, or 1 hour to 9 hrs, or 2 hrs to 8 hrs. In embodiments, the thermal annealed pellets have a dHf of at least 21 J/g, or at least 22 J/g, or at least 23 J/g, or at least 24 J/g, or at least 25 J/g, or at least 30 J/g, or at least 35 J/g, or at least 40J/g.
• the thermal annealed pellets have a dHf from 21 to 40 J/g, or from 22 to 40 J/g, or from 25 to 40 J/g, or from 21 to 35 J/g, or from 22 to 35 J/g, or from 25 to 35 J/g.
• the build compositions are preferably in powder form.
• the build composition may include 100% semi-crystalline polymer by volume based on the total volume of the solids fraction of the build composition, the semi-crystalline polymer may be in the form of a powder and the build composition is a semi-crystalline polymer in powder form.
• Additional but optional ingredients in the build composition include one or more of crystallizing agents such as nucleating agents;
• heat and/or light stabilizers such as heat absorbing inks; anti-oxidants, flow aids, and filler materials such as glass, mineral, carbon fibers and like.
• an important advantage of the build materials of the present invention is that they remain amorphous from the period immediately after being melted/sintered by the laser until they eventually vitrify as they are cooled below the semi-crystalline polymer’s glass transition temperature well after the build process is complete.
• This approach avoids the generation of mechanical stresses caused by crystallization. It also reduces the need for stringent control of temperature gradients across the surface or through the volume of the build. It also enables more of the sintering bed volume to be used and enable scaling up of the sintering bed sizes. It also enables the possibility of not cooling or rapidly cooling the build without the risk of curling or warping of sintered parts.
• the build materials of the present invention address these issues with processing of semi-crystalline polymers and still maintain the advantage of being
• an additive manufacturing method for producing a three-dimensional object including the steps of:
• the build material including a build composition in powder form that includes a semi-crystalline polymer
• each applying and directing step is much shorter than the minimum crystallization half time.
• the temperature of the part bed in the method of the present invention may vary more than 5°C over the said total time period for all the applying and directing steps.
• the additive manufacturing process can be a high-speed sintering (HSS) process.
• HSS process can include the steps of:
• a roller assembly deposits a layer of the powder on the print bed.
• the layer of powder is heated (before or after being deposited) to a temperature below the onset melting temperature.
• the RAM is an ink, capable of absorbing a specific form or energy such as infrared light, that is printed on the areas to be sintered.
• print heads can jet bitmap images onto the bed using the RAM.
• energy gets absorbed by the RAM, e.g., ink, heating the powder underneath it to above Tm and sintering the powder to a solid layer.
• an Infra-Red (IR) source e.g., lamp
• IR energy which causes the material to selectively melt and fuse together.
• the exposure of IR energy can be at the same time the RAM is being printed.
• the unprinted areas in the print bed remain a powder.
• the part (being formed layer by layer) can be lowered with the print bed and a next layer of powder can be spread onto the part and print bed, and the process repeated until the print is completed.
• Final sintered parts can then be removed from the powder bed.
• the present invention is directed to a polymer article formed via an additive manufacturing process, referred to herein as an additive-manufactured polymer article.
• An important feature of the present invention resides in the fact that the polymer of an additive-manufactured polymer article formed from the build material of the present invention is amorphous.
• the semi-crystalline polymers can be used to 3D print dental aligner thermoform molds (or arches) that can be used as molds to thermoform dental aligners using sheet material.
• the sheet material is clear.
• the dental aligner thermoform molds are printed by SLS-AM or HSS as described herein.
• dental aligners are prepared by a method that comprises: (i) taking a digital scan of a person in need of teeth alignment; (ii) calculating the different aligner shapes needed for that person; (iii) 3D printing thermoform molds (or arches) for the different aligners using one or more of the semi crystalline polymers described herein; and (iv) using the molds to thermoform the different aligners with a sheet material in a thermoforming process, e.g., vacuum forming.
• the semi-crystalline polymers (described herein) can be used to directly 3D print dental aligners, without the need to print thermoform molds, thus avoiding the thermoforming step described above.
• dental aligners are prepared by a method that comprises: (i) taking a digital scan of a person in need of teeth alignment; (ii) calculating the different aligner shapes needed for that person; (iii) 3D printing the different aligners using one or more of the semi-crystalline polymers described herein.
• the dental aligners can be subjected to post treatment processes to modify surface properties.
• such post treatments can include one or more of: flame treating the surface to improve surface smoothness or aligner visual clarity; impregnating the printed aligners with a chemical compound or resin to improve surface smoothness or aligner visual clarity; decorating the surface of the aligner with indicia or designs, e.g., by printing or applying a decorative film of sheet; or over coating the dental aligner with a liquid coating or film to change surface properties.
• the over-coating can include coating or laminating the surface of the aligner with another polymer or elastomeric material, e.g., silicone or polyurethane. In embodiments, the over-coating can provide a softer feel for the cheeks, lips and gums.
• Copolyesters in the below examples were manufactured via hydrolytic polycondensation according to standard methods.
• copolyesters typically comprise one or more diacids and one or more diols. The total number of moles of the all the diacids is equal to the total number of moles of all the diols.
• bulk pellets of commercial copolyesters were obtained and their compositions and physical properties are listed below in table 1 .
• Crystalline content is defined as the heat of fusion, AHf or dHf.
• Polymer 1 had a crystalline melting temperature of 187 °C.
• the amount of acetone needed to promote solvent crystallization was
• Solvent crystallization of the (pellet) core as a function of time was also investigated. 50 grams of Polymer 1 pellets was exposed to 10 parts acetone and 5 gram samples were removed every hour for 8 hours, as well as after 16 and 20 hours. Table 3 shows the dHf as a function of acetone exposure time. Table 3 - dHf as a function of exposure time.
• Parts were printed using a laser sintering process using Polymer 1 pellets that were manufactured using one-hour acetone exposure followed by drying (thermal annealing) at 140°C for 8 hours.
• the thermally annealed pellets were ground into a powder having a particle size of about 80 microns and printed using EOS sinterstation.
• the printed parts provided high resolution prints, the parts were brittle.
• the amount of acetone required to crystallize bulk pellets of Polymer 4 was determined to be less than ten parts. Similar to Polymer 1 (as shown in Table 2), the heat of fusion as a function of % acetone for Polymer 4 did not have a marked gain in crystallinity above 10 parts acetone. At 10 parts acetone, the dHF was about 1 1 J/g and it remained in a range from about 9 to less than 14 as the amount of acetone was increased up to 100 parts.
• TX2000 did not thermally anneal beyond the initial acetone induced crystallization. This was also apparent in the flex bar as the core of the bar remained transparent. Based on this, it appears that TX2000 did not meet the requirements of dHf and crystallinity required for laser sinter printing.
• TX1000 and TX1500HF increased in crystallization content as a function of thermal annealing time and plateaued after about 8 hours.
• TX1000 powder was also evaluated using DSC heating and cooling and plotting the DSC heat-cool-heat thermograms.
• the powder was formed from crystallized (initial solvent crystallized shell and then thermal crystallized) pellets that were cryogenically ground to a sub 100 micron particle size (as described herein).
• Figure 8 shows the DSC heat-cool-heat thermograms of solvent and thermally annealed TX1000 powder.
• TX1000 displays amorphous return behavior where induced crystallinity does not return upon cooling at 20 °C/min, as well as an amorphous second heat thermogram. TX1000 yields the behavior that would allow for laser sintering in a high temperature SLS printer due to the high dHf and the minimal transition at the glass transition temperature.
• the TX1000 powder (described herein) was also successfully printed on a PA12 centric printer using typical PA12 conditions.

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